Semiconducting metal oxides with the cubic ksbo&#39; 3 &#39;crystal structure

ABSTRACT

Oxides with the cubic KSbO3 crystal structure of the type Bi3GaSb2O11 are semi-conducting materials.

United States Patent UNITED STATES PATENTS 3,529,978 9/1970 Taylor etal. 252/521 X Bouchard et al. 1 Jan. 7, 1975 [541 SEMICONDUCTING METALOXIDES WITH 3,553,109 1/1971 Hoffman.....' 252/521 X THE CUBIC s o(:RYSTAL STRUCTURE 3,560,410 2/1971 Schubert 1 252/518 3,583,931 6/1971Bouchard 252/521 X 1 Inventors: Robert Josep B uchard, 2412 3,586,642(5/1971 Mutsuoet 111.... 252/521 x Shellpot D11; Arthur William3,681,262 8/1972 Bouchurd et a1. 252/521 X Sleight, 406 Nichols Ave.,both of 3,682,766 8/1972 Mather 1. 252/521 X Wilmington, Del. 19803 1[22] Filed: Dec. 18, 1972 Przmary ExammerStephen J. Lechert. Jr. 1 1 pp3161267 Assistant ExaminerR. E.'Schafer [52] US. Cl 252/519, 252/63.5,252/521, 252/518 [51] Int. Cl. H0lb l/08, HOlb 3/10 5 ABSTRACT [58]Field of Search 252/518, 519, 521,463,

Ox1des w1th the cub1c KSbO crystal structure of the [56] ReferencesCited type Bi GaSb O are semi-conducting materials.

12 Claims, No Drawings SEMICONDUCTING METAL OXIDES WITH THE CUBIC xsboaCRYSTAL STRUCTURE BACKGROUND OF THE INVENTION 1. Field of the InventionThis invention relates to new electrically semi conducting oxides havingthe cubic KSbO crystal structure. More particularly, it relates tosemiconducting oxides with the cubic KSbO crystal structure of the typeBi GaSb O The compositions contain bismuth or a mixture of bismuth plusa rare earth metal chemically combined with aluminum, gallium, iron,rhodium, ruthenium, antimony, or tellurium, and with eleven oxygenatoms.

2. Description of the Prior Art Metal oxides containing bismuth or amixture of bismuth and a rare earth metal chemically combined withvarious other elements such as gallium, chromium, tellurium and iron,etc., are known, e.g., BiGaTeO Bi 66020, BI4TI3O12, Bizwog, andBIY2Fe5O12. None of these, however, have the cubic KSbO structure.

SUMMARY AND DETAILED DESCRIPTION OF THE INVENTION M is a rare earthmetal of atomic number 57-71, in-

elusive;

M is aluminum, gallium, iron, rhodium or ruthenium;

M is antimony or tellurium;

x is a number in the range to about 1.5;

y is a number in the range 0 to 1; with the provisos that l. y 0 when Mis aluminum, gallium, iron or rhodium and M is antimony;

2. y when M is aluminum, gallium, iron or rhodium and M is tellurium;and

3. y 1 when M is ruthenium and M is antimony.

In the most preferred configuration in which x y O, the oxides are ofthe type Bi MM O e.g., Bi GaSb O Up to 50 mole preferably 33 mole of thebismuth atoms may be replaced by a rare earth metal of atomic number57-71, inclusive, such as lanthanum, gadolinium, etc.

The oxides of the present invention may be prepared by heating togethera mixture of the requisite ground oxides in amounts corresponding to themole ratios in the formula of the desired composition. Since the purityof the product reflects the purity of the reactants used, it ispreferred to use reactants having 99+% purity.

Exact stoichiometry is preferred for all metal oxide reactants with theexception of the bismuth oxide which may be present in excess.

The ground oxides are heated at a temperature range of 800-1 100C., apreferred range being 900-1000C. It is preferred to effect the reactionini.- tially in an open vessel. A second firing of longer duration athigher temperatures in evacuated sealedtubes can be carried out in orderto obtain single-phase products and remove remaining impurities.Platinum or mullite (3A1 O '2SiO crucibles open to the air inEMBODIMENTS OF THE INVENTION The following non-limitative examples willserve to illustrate the practice of the invention. All parts are byweight unless stated otherwise.

EXAMPLE I Biacasbzou The proportion of reactants utilized in Example 1correspond to those theoretically required for the production of Bi GaSbO i.e., 3Bi O 621 0;, 2Sb O 20,(air) 2Bi GaSb O For 1 hour, 0.9670 g ofBi O 0.1297 g of oa o, and

0.4033 g of Sb O were ground together in a mechanical agate mortar andpestle. The mixture was fired in an open platinum crucible in a mufflefurnace for sixteen hours during which time the highest temperature was1000C. The resulting sintered yellowish mass gave an X-ray patterncharacteristic of a cubic KSbO phase with a lattice parameter of 9.50 A.

EXAMPLE 2 BIgRUzSbO For 1 hour, 1.2584 g of ego, 0.4791 g of Ru0 and0.2624 g of Sb O were ground in a mechanical agate mortar and pestle.The weights used correspond to the molar ratios implied by the reactionequation, BBi O 4Ru0 -.lsmog", 2Bi Ru- SbO The mixture was pressed intoa pelle'f'a'nd tired to 1000C. in oxygen for 16 hours. The pellet wasthen sealed in a platinum tube under vacuum and refired'to ll00C. for 5days. The product was a brown, single-phase material with a latticeparameter of 9.4248 0.008 A.

EXAMPLE 3 Bi RhSb O For 1 hour, 0.7903 g Bi O 0.2152 g Rhgo3, and 0.4944g of Sb O were ground in a mechanical agate mortar and pestle. Theweights used correspond to the molar ratios implied by the reactionequation, 3Bi O Rh O 2Sb O 2Bi RhSb,O

The mixture was pressed into a pellet and fired to l00OC. in oxygen for20 hours, sealed in a platinum tube under vacuum, and refired to ll00C.for 5 days. The product was a brown, single-phase material with alattice parameter of about 9.51 A.

EXAMPLE 4 Bi ALSb o For 1 hour, 0.9813 g of Bi,0,, 0.1095 g of Al,O -3-H,O, and 0.4092 g of Sb O were ground in a mechanical agate mortar andpestle. The weights used correspond to the molar ratios implied by thereaction equation, 3Bi 0 A1,O -3I-I,O 2Sb 0 f 2Bi AlSb,O The mixture waspressed into a pellet and fired to 1000C. for 16 hours. The pellet wasthen sealed in a platinum tube under vacuum and refired to 1100C. fordays. The product had an X-ray pattern correspond ing to a cubic KSbOtype phase with a lattice parameter of 9.45 A, plus a trace of animpurity phase.

EXAMPLE 5 Bi FeSb O For 1 hour, 6.3409 g of Bi O 0.7243 g of Fe O and2.9347 g of Sb O were ground together in an agate mortar and pestle. Theweights correspond to the molar ratios in the reaction equation 3Bi O FeO 2813205 2Bi3FeSb20n.

The mixture was placed in a mullite crucible which was placed in amuffle furnace. The temperature was held at 700C. for hours. The samplewas removed from the crucible and reground in an agate mortar andpestle. The reground sample was replaced in the same crucible and heatedat 900C. for .ten hours in the muffle furnace. An X-ray diffractionpowder pattern showed a predominant cubic KSbO -type phase with alattice parameter of 9.524 A.

EXAMPLE 6 3 L61 L33 1l For 1 hour 6.1408 g Bi O 1.1691 g of Fe O and2.6901 g HTeO '2l-1 O (telluric acid) were ground together in an agatemortar and pestle. The weights correspond to the molar ratios in thereaction equation, 9Bi O 5Fe O 8H leO -2H O 6Bi Fe, -,Te 33011 241-1 01The mixture was placed in a mullite crucible in a muffle furnace. Thetemperature was held at 800C. for 10 hours. The product was a brownpowder whose X-ray diffraction powder pattern showed a predominant cubicKsbO -type phase with a lattice parameter of 9.473 A.

EXAMPLE 7 Bi LaGaSb O For l hour, 1.3363 g of Bi O 0.4672 g La O '0.2688

g Ga O and 0.9277 g Sb O were mixed together by grinding in an agatemortar and pestle. The weights correspond to the molar ratios implied bythe reaction equation, 2Bi O La O Ga O 2Sb O 2Bi LaGaSb O The mixturewas placed in a mullite crucible in a muffle furnace. The temperaturewas held at 1000C. for 10 hours. The product was a white powder. AnX-ray diffraction powder powder pattern showed a predominant cubic KSbO-type phase with a lattice parameter of 9.512 A.

EXAMPLE 8 Blg GdGasbzon inant cubic KsbO -type phase with a latticeparameter of 9.457 A.

EXAMPLE 9 Single Crystal of Bi GaSb O For 30 minutes, 16.7744 g Bi O (a500% molar excess), 0.8744 Sb O and 0.5624 g Ga O were ground togetherwith a mechanized agate mortar and pestle. The mixture of ground oxideswas fired in an open platinum crucible in a muffle furnace to 1060C. Onreaching this temperature, the mixture was cooled at a rate ofapproximately 2C per hour to approximately 700C and then removed fromthe furnace. The product was leached with 1:1 HNO to remove excess Bi OSome transparent crystals in the 3-5 mm range were observed. X-raypatterns of these crystals were typical of the cubic KSbO crystalstructure with all lines indexing similarly (a, 9.45 A.). A'Gunier x-rayphotograph of a single crystal showed a phase having a lattice parameterof 9.4907 1- .0002 A.

The metal oxides of the present invention are useful for a variety ofdielectric applications. The compounds possess high dielectric constantswhich are independent of temperature and also possess low dissipationfactors. Temperature invariance of dielectric constants is a veryunusual property since most good dielectrics have dielectric constantswhich depend strongly on temperature.

For example, capacitor dielectrics generally fall into two categories:the first which has a relatively temperature-independent dielectricconstant, but whose dielectric constant is very low (5-10). Suchmaterials as electrical porcelain and mica fall into this class. Thesecond category includes materials like BaTiO which have very highdielectric constants 1000 which is desirable, but are extremelytemperature dependent, which makes them useless as circuit elements intuning or resonance circuits since small, normally unavoidable changesin ambient temperature throw the circuit out of resonance.

The compositionsof this invention are also useful for screen-printabledielectric applications. A requirement for this application is that thematerial, after printing in a pattern through a screen, sinters toadense, adherent film under firing conditions commonly employed in thethick film industry, i.e., belt furnaces with top temperatures in the10001050C. range. It is somewhat unusual to find a material which hasthese properties, especially without the addition of any low-meltingbinders. For example, BaTiO dielectric has to be fired at temperaturesgreater than 1200C. to achieve sintering, so it is completely unsuitablefor screen-printable applications.

EXAMPLE A Measurements for dielectric constants and dissipation factorswere performed with a capacitance bridge on Bi GaSb O both in sinteredpellet form and in the form of a single crystal. These results arelisted in the table.

Dielectric Constants and Dissipation Factors of Bi Gasb o Form ofFrequency Dielectric Dissipation Compound (Hz) Constant (K') Factor(DF) 1. Single 10 69.6 0.0080 Crystal 10 68.7 0.0038

68.3 0.0021 2. Sintered 10" 30 0.0001 Pellet 10 30 0.0006

wherein Mis a rare earth of atomic number 57-71 inclusive; M isaluminum, gallium, iron, rhodium or ruthenium; M is antimony ortellurium; x is a number in the range 0 to about 1.5; y is a number inthe range 0 to 1; with the provisos that 1. y 0 when M is aluminum,gallium, iron or rhodium and M is antimony; 2. y when M is aliminum,gallium, iron or rhodium and M is tellurium; and 3. y 1 when M isruthenium and M is antimony. 2. A metal oxide according to claim 1 inwhich y O.

3. The metal oxide according to claim 1 in which has the formulaBigGasbzon.

4. The metal oxide according to claim 1 which has the formulaBiaRuzsbou.

5. The metal oxide according to claim 1 which has the formula 6. Themetal oxide according to claim 1 which has the formula 7. The metaloxide according to claim 1 which has the formula 8. The metal oxideaccording to claim 1 which has the formula 9. The metal oxide accordingto claim 1 which has the formula Bi LaGaSb O 10. The metal oxideaccording to claim 1 which has the formula BigGdcasbgou.

11. A dielectric composition comprising a metal oxide of claim 1.

12. A dielectric composition comprising the metal oxide of claim 3.

1. A SEMICONDUCTING METAL OXIDE OF CUBIC KSBO3 CRYSTAL STRUCTURE HAVINGFORMULA BI3-ZMZMI 1+YM2 2-YO11 WHEREIN M IS A RARE EARTH OF ATOMICNUMBER 57-71 INCLUSIVE; M1 IS ALUMINUM, GALLIUM, IRON, ROHODIUM ORRUTHENIUM; M2 IS ANTIMONY OR TELLURIUM; X IS A NUMBER IN THE RANGE 0 TOABOUT 1.5; Y IS A NUMBER IN THE RANGE 0 TO 1; WITH THE PROVISOS THAT 1.Y=0 WHEN M1 IS ALUMINUM, GALLIUM, IRON OR RHODIUM AND M2 IS ANTIMONY; 2.Y=2/3 WHEN M1 IS ALIMINUM, GALLIUM, IRON OR RHODIUM AND M2 IS TELLURIUM;AND
 2. y 2/3 when M1 is aliminum, gallium, iron or rhodium and M2 istellurium; and
 2. A metal oxide according to claim 1 in which y
 0. 3.The metal oxide according to claim 1 in which has the formulaBi3GaSb2O11.
 3. y 1 when M1 is ruthenium and M2 is antimony.
 3. Y=1 WHENM1 IS RUTHENIUM AND M2 IS ANTIMONY.
 4. The metal oxide according toclaim 1 which has the formula Bi3Ru2SbO11.
 5. The metal oxide accordingto claim 1 which has the formula Bi3RhSb2O11.
 6. The metal oxideaccording to claim 1 which has the formula Bi3AlSb2O11.
 7. The metaloxide according to claim 1 which has the formula Bi3FeSb2O11.
 8. Themetal oxide according to claim 1 which has the formulaBi3Fe1.67Te1.33O11.
 9. The metal oxide according to claim 1 which hasthe formula Bi2LaGaSb2O11.
 10. The metal oxide according to claim 1which has the formula Bi2GdGaSb2O11.
 11. A dielectric compositioncomprising a metal oxide of claim
 12. A dielectric compositioncomprising the metal oxide of claim 3.